A compact disk (hereinafter, referred to as a CD) has been widely used to record a large amount of digitized sound and image information. The substrate of the CD is made of transparent synthetic resin on the surface of which a large number of so-called pits are formed in accordance with digital information of "1" or "0". An aluminum thin film layer having high light reflectivity is deposited on the thus formed surface by use of a sputtering technique. The thus recorded information is read by the presence or absence of the reflected light of a laser light beam applied to the CD.
The aluminum thin film deposition of a single substrate can be performed in a relatively short period. Thus, a continuous film deposition with respect to a large number of substrates can be achieved.
As shown in FIG. 9, in a conventional substrate loading apparatus 95, a disk substrate 81 is transferred and loaded in a film-deposition chamber 80, which is a vacuum chamber, by use of a suction head 87. The suction head 87 serves both to transfer the substrate 81 and to hermetically seal the film-deposition chamber 80. A plurality of suction pads 87a which hold substrate 81 by sucking are provided on the suction head 87. The suction head 87 is fixed to a rotating shaft 86 which is rotatable in a direction indicated by arrow X3, and is movable vertically in a direction indicated by arrow Y3. These rotational and vertical motions of the shaft 86 can be achieved by use of a drive mechanism 82 including a motor 83 and a gear arrangement 84, and an air cylinder 85. The suction pads 87a are connected to an external exhaust system 91 by way of an exhaust-and-intake passage 88 formed piercing through the suction head 87 and rotating shaft 86, an outlet 89, and a pipe 90.
The external exhaust system 91 serves as an operation source which causes the suction pads 87a to capture and release substrate 81. The system 91 comprises a bifurcated pipe 92, valves 93a and 93b, and an exhaust pump 94 such as a vacuum pump.
Assume that the above-described substrate loading apparatus 95 receives substrate 81 from a plurality of suction pads 96 of a conveyor-type transferring apparatus (not shown), and loads the thus received substrate 81 in the film-deposition chamber 80 shown in FIG. 10. In this case, the valve 93a is opened so as to cause the suction pads 87a to capture substrate 81. The rotating shaft 86 is driven by the motor 83 to rotate by about 180 degrees. As a result, the thus captured substrate 81 is caused to face the film-deposition chamber 80.
Next, suction head 87 is moved down toward film-deposition chamber 80 by use of the air cylinder 85. Thereafter, valve 93a is closed, and valve 93b is opened to introduce the atmosphere. As a result, substrate 81 is transferred in film-deposition chamber 80.
In the above-described conventional substrate loading operations, the repetitive vertical and 180 degree-rotational motions of rotating shaft 86 and suction head 87 are performed whereas the external exhaust system 91 is fixed to the ground. Thus, pipe 90, whose one end is fixed to the external exhaust system 91 and the other end is fixed to the rotating shaft 86, inevitably experiences the torsional reciprocating motions associated with vertical motions.
To alleviate the stress-strain of pipe 90 in the above-described operation, the length of pipe 90 must be increased. However, the lengthy pipe 90 has disadvantages such that a large space is required for pipe 90 to achieve the torsional swiveling motions. Further, these motions of pipe 90 are dangerous for the operator.
Moreover, the inertia moment of the heavy suction head 87, which moves repeatedly in turn-over reciprocating motions, applies undesirable load to the motor 83 and gear arrangement 84. Such inertia moment can cause the overload of motor 83 and the wear of gears.
Further, in the conventional substrate loading apparatus, suction head 87 carries only a single sheet of substrate 81 at a time. Thus, the loading cycle speed of the apparatus can be increased only by the increase of the rotation speed of the drive mechanism 82. This inevitably limits the increase of the loading cycle speed. Therefore, the improvement of the loading apparatus has been desired.
FIG. 10 shows the conventional film-deposition chamber 80 which comprises an upper wall plate 98, a load-lock section 99, and a sputtering section 100. Further, a load-lock chamber 101 is formed in the upper wall plate 98 at a position over the load-lock section 99.
The load-lock chamber 101, which is shown in an enlarged cross-sectional view of FIG. 11, serves as a boundary chamber between the atmospheric pressure and a vacuum when substrate 81 to be sputtered is delivered to a susceptor 102 from suction head 87 or when sputtered substrate 81 is delivered to suction head 87 from susceptor 102. A passage 103, which serves both to exhaust and intake, is formed in the upper wall plate 98. The passage 103 is connected to an external rotary pump 105 through a bifurcated pipe 104, a valve 106a and a pipe 109.
When substrate 81 is delivered to susceptor 102 from suction head 87, valve 81 is opened to coarsely exhaust load-lock chamber 101 to a vacuum of an intermediate degree, which is against the sucking force of suction pads 87a. Thus, substrate 81 can be delivered to susceptor 102 from suction head 87. Thereafter, a transferring table 107, to which susceptor 102 is fixed, is moved downward. Further, film-deposition chamber 80 and load-lock chamber 101 are still exhausted to a vacuum of a higher degree by use of an exhaust vent 108.
Further, when, after finishing sputtering process by facing a mask 116 of sputtering chamber 115, the film deposited substrate 81 is delivered to suction head 87 from susceptor 102, the other valve 106b, which is interposed between the bifurcated pipe 104 and the atmosphere through a pipe 110, as shown in FIG. 12, is temporarily opened to introduce the atmospheric pressure into load-lock chamber 101. Thereafter, substrate 81 is captured by suction pads 87a, and is transferred to the outside. In FIG. 11, reference characters L represent o-rings for sealing.
In the above-described conventional substrate loading apparatus, substrate 81 is held by suction pads 87a and a ring-shaped rim 111 formed in the periphery of suction head 87, as shown in FIG. 11. This is because suction head 87 must hold substrate 81 without touching its surface on which information has been recorded.
However, the conventional substrate loading apparatus has the following disadvantages. Specifically, when sputtered substrate 81 is delivered to suction head 87 from susceptor 102, the pressure in load-lock chamber 101 is changed to the atmospheric pressure. On the other hand, substrate 81 has been captured by suction pads 87a and in close contact with rim 111. This forms a hermetically sealed space 112 interposing substrate 81 for a certain period, and the pressure in the space 112 differs from the atmospheric pressure in this period. Thus, substrate 81 might be deformed by bending into a shape illustrated by the dotted line 113. As a result, the information-recorded surface of substrate 81 might be directly touched to suction head 87 and damaged. Such damage to the information-recorded surface of substrate 81 can also occur even when substrate 81 is delivered to susceptor 102 from suction head 87. This is because susceptor 102 receives substrate 81 in a plane-contact manner. Even a minute scar on the information-recorded surface of substrate 81 causes substrate 81 per se to be a defect. Thus, the improvement, in which such undesirable damage that can occur in the process of transferring is avoided, has been desired.
Moreover, in the conventional substrate loading apparatus, suction head 87, to which pipe 90 for exhaust and intake is connected (see FIG. 9), is moved in turn-over reciprocating motions. Thus, a large space is required for the movement of pipe 90, and a heavy load is repeatedly applied to suction head drive mechanism 82. Further, substrate loading is performed in a sheet-by-sheet manner. Thus, the speed increase of substrate loading is inevitably limited. If an attempt is made to increase the speed of substrate loading, the load applied to suction head drive mechanism 82 is still increased.
Furthermore, in the conventional substrate loading apparatus, the information-recorded surface of substrate 81 might be damaged while being received and delivered in load-lock chamber 101 because of deformation caused by the pressure difference between both sides of substrate 81.